Grinding machine



Jan. 259 1944. S. gE, lWQQDBURY ET A1. 213409096 GRINDING MACHINE FiledJan. 26, l942 3 Sheets-Sheet l I5 Sheets-Sheet 2 /lllllllIII/IIlI/I/IIIM W i GRINDING MACHINE Filed Jan. 26, 1942 S. E. WOODBURY ET AL jan. 25,i944.

jxn- 25, 1944- s. E. wooDBuRY ETAL 2,34095 GRINDING MACHINE Filed Jan.26, 1942 3 Sheets-Sheet 5 im I Zin/enfans I Patented Jan. 25, 1944GRINDING MACHINE Stephen E. Woodbury and Stephen E. Woodbury, Jr..Beverly. Mass., assignors to Reid Brothers Company, Inc., BeverlyMassachusetts Mass., a corporation of Application January 26, 1942,Serial No. 428,174

4 Claims.

This invention relates to a grinding machine and more particularly to asurface grinding mations of parts hereinafter described and particularlydefined in the claims at the end of this specification.

In the drawings illustrating the preferred embodiment of the invention,Fig. 1 is a plan view, with portions broken away, of a grinding machineembodying the present invention; Figs. 2 and 3 are detail views ofdriving connections to the cross feed mechanism, to be referred to;

mechanism for controlling the driving mechap nism, as hereinafterdescribed.

In accordance with one feature of the present invention, provision ismade for operating the reciprocable work supporting table throughconnections from a reversing motor arranged to be controlled by themovement of the table. Provision is also made in the motor circuit fordecreasingthe starting torque of the reversing motor whereby to reducethe shock incident to the change in direction and to contribute inproducing smoother table operation and also to reduce to a minimumexcessive heating incident to rapid reversal of rotation of the motor.As a further provision for assuring smooth and substantiallyvibrationless table operation, the connections to the table may includesteel bands or straps arranged to be alternately wound and unwound upona drum, as will be described.

wheel I2 and a longitudinally reciprocablc work supporting table I4. Thework supporting table is mounted to slide longitudinally upon ways I6,I8 provided in a cross slide 20 which, in turn, is adapted to be movedtransversely in ways 22, 24, formed in the top of a casing 26 mountedupon 'the base 28 of the machine. The grinding wheel I2 is mounted upona spindle I3 and is independently driven by a spindle motor |5, as shownin Fig. 7.

The work supporting table I4 is arranged to be reciprocated throughconnections including a driving pulley or drum 30 and two steel bands orstraps 32, 34, each of which is connected at one end to the drivingdrum, as illustrated in detail in Fig. 5. The other ends of the strapsextend over idler pulleys 36, 38 respectively, and are connected to lugs40, 42 depending from the opposite ends of the table, as shown in Fig.4. The idler pulleys 36, 38 are rotatably mounted upon studs 44, 48supported in the cross slide 20.

Provision is made for driving and reversing the rotation of the drum 30to cause the straps 32, 34 to alternately Wind and unwind on the drum toeffect reciprocation of the table I 4 through connections from areversing motor 50 as shown in Figs. 1 and 4. The drum 30`is mountedupon and arranged to rotate with a driving shaft 52 journaled insuitable bearings .54, 56 mounted in the machine frame. The shaft 52 isprovided with a gear 58 fast thereon which is arranged to mesh with apinion 60 formed integrally with a clutch member 62 rotatably mountedand longitudinally movable upon a shaft 64. The clutch member 62 isarranged to be moved into operative engagement with a clutch member 65fast on the end of a shaft' 61 suitably journaled in a gear casing 'IDformed integrally with the motor supporting bracket 12. The shaft 6l isprovided with a worm wheel 14 fast, thereon arranged to cooperate with aworm gear I6 secured to the motor shaft 18.

In the illustrated embodiment of the invention, provision is made fordisengagirm the movable clutch member 62 from the power driven member 65when it is desired to move the work supportingtable manually, and asReferring now to the drawings, and particularly to Fig. 4, the grindingmachine indicated generally at I0 is provided with a grinding hereinshown, the clutch member 62 is arranged to engage a cooperating memberfast on the shaft 64, which latter is provided with a hand wheel 82 atits outer end. The shaft 64 is jour- ,naled in a. bearing 83 formed in abracket 84 detachably secured to the casing 26. The movable clutchmember 62 is moved longitudinally to engage and disengage the clutchc'onneciions t5, B by a shifter member 86 adapted to be actuated throughconnections to a hand lever 88, as illustrated in Fig. 1. The pinion 60is made wide enough to cooperate with the gear 58 in either of itslongitudinally movable positions. As herein shown, the clutch shifterunit, indicated generally at 90, is carried by the detachably mountedmotor bracket 'I2 to form an assembled unit therewith.

From the description thus far, it will be observed that the detachablebracket 12 carries the motor driving mechanism and the clutch shiftingmechanism as a completely assembled unit which may be convenientlyassembled prior to attachment to the casing 26 of the frame. Thisconstruction saves time in the assembly operation, renders the partsmore accessible for replacement and repair, and results in economy andexpediency in manufacture, In assembling the unit, it will be observedthat the4 shifter member 86, which may be' forked, is arranged to bereceived in a grooved portion 92 of the member 62. The unit is attachedto the casing 26 by screws 84.

Referring now to Figs. 1, 2 and 3, provision is made in the preferredembodiment of the invention for progressively advancing or retractingthe longitudinally reciprocable work table in a transverse directionduring the operation of the machine. As herein shown, the cross slide 20is provided. with a bracket 9S attached to and depending from theunderside thereof. A square threaded screw 98, secured at one end to thebracket 96, is arranged to be received in an internally threaded bushingor hollow shaft which in turn is rotatably mounted in a hub |02 formedin the casing 26.

Provision is made for intermittently rotating the hollow internallythreaded shaft |00 in either direction to effect transverse movement ofthe table during the operation of the machine. ris herein shown, thehollow shaft is arranged to be rotated through connections including acrank member |04, a rack |06 connected to and arranged to bereciprocated by the crank, and a gear |03 loosely mounted on the hollowshaft and cooperating with the rack |06. The loosely mounted gear isformed integrally with a pawl carrier ||0 upon which is mounted a doublepointed pawl ||2 arranged to cooperate with a square toothed ratchet 4keyed to the hollow shaft, as illustrated in Fig. 2. Provision is madefor adjusting the double pointed pawl ||2 to engage either one or theother of the points with the square toothed ratchet, or to position thepawl in a neutral position. Such adjustment may be effected through aspring pressed ball arranged to be received in depressions in thecarrier, as indicated at ||6 in Fig. 2, and may be moved from oneposition to another by rotating the knob ||8. A hand wheel ||8 alsosecured to the hollow shaft 00 is provided to permit manual operation ofthe transverse mechanism when the pawl ||2 is in neutral position.

In operation, when it is desired to eiIect intermittent rotation of thehollow shaft |00 in a counterclockwise direction, the pawl |I2 may bepositioned as indicated in Fig. 2 'so that when the pawl carrier ||0 isrotated in this direction by the reciprocating rack |06 and the gear|00. the pawl ||2 in engagement with the ratchet will rotate the hollowshaft in a counterclockwise direction. On the return stroke of therackiil, the pawl will slide over the ratchet teetl-. It will be clearthat when the pawl is positioned to engage the second point thereof withthe square toothed ratchet, rotation of the hollow shaft |00 in thereverse direction will be effected. Thus it will be seen that theinternally threaded hollow shaft |00 in cooperation with the squarethreaded screw is operative to effect transverse movement of the crossslide 20 and the table I4 supported thereon, in either direction duringthe operationof the machine. As illustrated in Figs. 1 and2,the'reciprocated rack |06 is received in a guide |20 formed integrallywith a sleeve |22 loosely mounted upon the hollow shaft |00 to permitrelative movement of the-supporting sleeve |22 during the angularmovements of the rack |0E`as reciprocated by the crank |04.

Referring now to Figs. 1 and 3, the mechanisrn for rotating the crankmember |04 will be described. As therein shown, the crank member isclamped fast upon the end of a stud |24, rotatably mounted in a bearing"|26 formed in the bracket 84. 'I'he stud |24 extends from and is formedintegrally with a, pawl carrier |28 in which two pawls |30, |32 aremounted and arranged to cooperate with a square toothed ratchet |34. Thesquare toothed ratchet |34 is formed integrally with and is arranged torotate with the driving gear 58. As above described, the driving gear 58is arranged to change its direction of rotation during the operation ofthe machine.- Thus, in operation, when the ratchet |34 is rotated in aclockwise direction, the pawl |30, see Fig. 3,. will be operative torotate the crank through a predetermined stroke until the tail of thepawl engages a pawl stop |36 extending from the bracket 84, see Fig. 7,to disengage the pawl |30 from its ratchet |34. Thereafter, during theremainder of the clockwise movement of the ratchet I 34, the other pawl|32 will slip over the ratchet teeth. When the direction of rotation ischanged, the pawl |32 becomes effective to rotate ythe crank as abovedescribed, until it in turn is disengaged from the ratchet by the pawlstop |38. Thus it will be seen that each time the crank is rocked ineither direction the rack |03 is reciprocated to effect rotation of thehollow shaft |00 in the desired direction as determined by the adjustedposition of the double pointed pawl ||2. The rack |06 is secured to thecrank |04 in a T-slot |05 to permit convenient adjustment of the lengthof stroke.

From the description thus far it will be observed that the detachablebracket 84 carries the crank driving mechanism and the connections formanually operating the machine as a completely assembled unit which maybe conveniently assembled prior to afllxing the bracket to the casing28. Thus, the assembly oi' this portion of the machine is facilitated,the parts rendered more accessible for adjustment or replacement and thestructure results in economy in manufacture.

Provision is made for permitting lateral movement 'of the driving drum30 on its shaftl 52 during the transverse movement of the cross slide20. As herein shown, the shaft 52 is provided with three raceways |40 inwhich ball bearings |42 disposed in the drum 30 are arranged to run. Asshown in Fig. 6, the ball bearings are retained in the drum by springwire rings arranged to be received in grooves |44 provided in the drum.The rings may be open to enable them to be contracted and forced intothe grooves where they may again expand into a position to preventescape of the lball bearing members from the drum. Thus, it will be seenthat the bearing members |42 serve as a driving connection between theshaft 52 and the drum 30 and also permit lateral movement of the drum lna smoothly operating manner, thus reducing friction and tendency to bindon the shaft to a minimum. As shown in Figs. 1 and 4, the bracket Q6,attached to the cross slide 20, is provided with arms M5, Nt arranged toembrace the drum 30. and to move it along the shaft 52 in alignment withthe longitudinally reciprocabletable Il as the cross slide is movedtransversely.

Referring now to Figs. 1 to 8, provision is made for controlling thereversible motor 50 to effect a change in direction of rotation thereofthrough connections from the reciprocable work table |41. As hereinshown, a reversing switch |50 mounted in the cross slide 2|) is arrangedto be operated by dogs |52, |54, adjustably supported upon and movablewith the table I4. The reversing switch comprises a slidingly mountedstud |56 arranged to be reciprocated by a pivotally mounted arm ittwhich is received in a slot in the stud |56. An operating arm I, fast onthe pivot shaft H52 is provided with pins |54, |65, arranged to beengaged by the dogs |52, |54, respectively, at the end of thepredetermined longitudinal movement of the table. The switch stud |55 isprovidedwith contacts |53, |11) and in operation, when a dog engages theswitch l50, it operates to first open the prevailing circuit to themotor 0 and then close a second circuit to operate the motor in areverse direction. .A handle itl is also provided on the -operating arm|55 to permit the switch to be manually operated when desired. A safetyswitch, indicated at |12, may also be provided to be operative to openthe entire circuit in the event the dogs |52, H54 areremoved or becomeloosened. As illustrated in Fig. Il, cam pieces |14, |16 supported onthe underside of the table lll are arrangedA to engage and depress theswitch member |12 to open the circuit at contacts |18 when the tableoverrides or fails to engage the reversing switch |50. The reversingswitch may and preferably will be of standard construction. A

As illustrated in Fig. 8, the wiring diagram therein shown includesconnections to the grinding head motor l5, and to the reversing motor50. Stop and start switches |82, |84 are arranged to open and close acircuit to a primary magnetic switch |85 which closes the circuits tothe grinding head motor and to the reversing motor at contacts |86, |81,|88 and |89. The reversing switch, indicated at |50 operates toalternately open one circuit and close another to the magnetic switches|90, |92 for alternately opening and closing the circuits to thereversing motor 50 at contacts |94, |95, |96, |91, whereby to reversethe direction of the current through the motor so that its direction ofrotation is reversed. The safety switch is indicated at |12 and amanually operated switch |98 may also be provided for opening thecircuit to the reversing switch |50. It will be observed that the wire2||l is preferably led through contacts 2|2, 2|4 of the reversing switchin order to open the circuit through all three wires 2|0, 2li, 2|8simultaneously when the on and off switch 22C is turned off.

Thev table driving motor 50 is preferably of the squirrel-cage polyphaseinduction motor type and is started by placing the same directly acrossthe line and is stopped and reversed by reversing the connections to twowires of the primary winding 200 of the motor at the time the motor isstill operating at full speed in the original direction. 'I'his motor isrequired to develop considerable power since in addition to overcomingthe friction load of the table it must also overcome the inertia'loadthereof during rapid starting and stopping as well as the inertia loadof the motor rotor, which may be comparable in amount to the inertiaload of the table. During the stopping operation the voltage developedby continued rotation of the motor in its original direction due toinertia after the connections to the motor have been reversedeffectively adds to the applied voltage to increase the current insteadof opposing the applied voltage as in motors under normal operation.

' Standard motors have been found to take excessive current withresulting overheating under these conditions and to produce torque whichis too-high resulting in too rapid stopping and reversal with constantdeleterious shocks and jars to the machine parts. Complicated controlcircuits such as those involving insertion of resistance into the motorcircuit under starting and reversing conditions are not satisfactorybecause of added expense and also because of failure of the controlsystem under rapid repetition of op eration. Increasing the size of astandard motor does not solvevthe problem, as this increases the inertiaload because of the larger size rotor required.

.It has been found that the structure of the motor itself can bemodified to reduce the starting and reversingcurrent and torque. Thismay be accomplished bykincreasing the number of turns in each phase ofthe primary winding of the motor 5U for a given applied voltage-so as todecrease the current as well as the torque during starting andreversing. In standard motors the number of turns in the primary windingis such that the flux necessary to develop a back volta-ge substantiallyequal to the applied voltage is just slightly less than that which willsaturate the iron of the motor in the portions of the iron havingmaximum flux density. That is to say, in a standard motor the maximumflux is just slightly less than that which will pass the knee of themagnetization'curve of the iron. By substantially doubling the number of-turns normally employed for a given voltage and iron structure, forexample using approximately 1% to 21A times the number of turns usuallyemployed, the flux necessary to produce a back voltage substantiallyequal to the applied voltage is reduced, the flux being substantiallyinversely proportional to the number of turns in the primary Winding. Byemploying a primary winding which results in a iiux which is notsubstantially greater than one-half of that necessary to producesaturation it has been found that the motor starts and reverses smoothlywithout tak-1 ing excessive current.

With the motor employed in the present invention in which the number ofturns in the primary winding is increased, the lesser amount of fluxcauses the torque during starting and reversing to be materially reducedand as the speed is low under these conditions the internal power totalstarting and reversing current is therefore materially reduced. Thiscurrent may be considerably greater than full load current under steadyload conditions but is much less than that taken by standard motorshaving primary windof said iron so as to provide a torque eliminatingings designed to operate with the iron adjacent the air gap nearly atsaturation during periods of maximum iiux. Thus the motors employed inthe present invention do not overheat and also develop a relatively lowreversing and starting torque, producing smooth operation of the machinewithout jar or shock. It will be seen that the. motor forming a part oi!the present invention is particularly adapted for the operation ofmachines having reciprocating tables with the motor'electricallyconnected directly to a power line and mechanically connected to thetable without intermediate reversing mechanisms so as to start, stop andreverse the table by merc reversal of the electrical connections.

'While the invention is particularly useful in connection with agrinding machine embodying a reciprocable work supporting table anddrivin-g mechanism including a reversing induction motor of thecharacter described, nevertheless viewed in its broader aspects theinvention may include other types of machines wherein a reversibleelement, either of the reciprocating, rotating, or oscillating type, isarranged to be driven by a reversing induction motor having thecharacteristics and in the manner above described.

While the preferred embodiment of the invention has been hereinillustrated and described, it will be understood that the invention maybe embodied in other forms within the scope of the following claims.

Having thus described the invention, what is claimed is:

1. In a grinding machine, in combination, a longitudinally reciprocablework supporting table, driving mechanism for reciprocating said tableincluding a. reversing motor of the induction type having a primarywinding, an electrical circuit for said motor for connecting saidprimary winding directly to a power line to apply full line voltage tolsaid motor during starting and reversing of said motor, a switch insaid circuit for effecting reversal of said motor, means carried by saidwork table for operating ,said switch when the table is moved apredetermined distance in either direction, the primary Winding of saidmotor being wound to produce a maximum flux in the' iron of said motornot substantially greater than half that causing saturation abruptreversal and insuring smooth starting movement.

2. In a grinding machine, in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor oi the inductiontype having a primary winding, means forautomatically controlling the reversing oi' said motor` to reciprocatesaid table, said means applying full line voltage to said primarywinding during reversing of said motor, said primary windingbeingprovided with substantially twice the number of turns which will producea maximum iiux in the iron causing saturation thereof, whereby thecurrent taken by said motor is maintained below that which will causeoverheating and the torque produced by said motor during starting andreversing is suiilciently low to eliminate abrupt reversal and insuresmooth starting movement.

3. In a grinding machine, in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor of the induction type having a primary winding, meansfor automatically controlling the reversing of said motor to reciprocatesaid table, said means applying full line voltage to said primarywinding during reversing of said motor, Ithe primary winding of saidmotor being wound to produce a maximum iiux in the iron of said motornot substantially greater than half that causing saturation of said ironso as to provide a torque eliminating abrupt reversal and insuringsmooth starting movement.

4. In a machine tool, in combinatiom'a work holding member and a toolmember, one of said members being movable relative to the other member,driving mechanism for movin-g said one member alternately in oppositedirections including a reversing motor of the induction type having aprimary Winding, means for automatically controlling the reversing ofsaid motor to alternately drive said one member in opposite directions,said means applying full line voltage to said primary Winding duringreversing of `said motor, the primary winding of said motor being woundto produce a maximum'ux in the iron of said motor not substantiallygreater than half that causing saturation of said iron so as to providea torque eliminating abrupt reversal and insuring smooth startingmovement.

STEPHEN E. WOODBURY. STEPHEN E. WOODBURY, JR.

